1. Chapter 1 Our Place in the Universe
“Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”
Douglas Adams, The Hitchhiker's Guide to the Galaxy English humorist & science fiction novelist ( )
“Galactic Stress” by David Levine, available for free online:
The opening scene to the movie Contact:

2. Chapter 1 Our Place in the Universe

3. 1.1 Our Modern View of the Universe
Our goals for learning:
What is our place in the universe?
How did we come to be?
How can we know what the universe was like in the past?
Can we see the entire universe?

4. What is our place in the universe?
Our main goal is simply to understand the basic hierarchy of structure from planet to solar system to galaxy to universe. This slide shows a lot about human history. E.g., we first learned that Earth is a sphere some 2,500 years ago; we learned that Earth is a planet going around the Sun only about 400 years ago; and we learned that the Milky Way is only one of many galaxies with the work of Hubble some 80 years ago…
Here at the beginning of the semester, our main goal is simply to make sure that students understand the basic hierarchy of structure from planet to solar system to galaxy to universe (clustering is less important at this stage). You might also wish to note that this slide shows a lot about human history. E.g., we first learned that Earth is a sphere some 2,500 years ago; we learned that Earth is a planet going around the Sun only about 400 years ago; and we learned that the Milky Way is only one of many galaxies with the work of Hubble some 80 years ago…

5. Star
A large, glowing ball of gas that generates heat and light through nuclear fusion

6. Planet
Mars
Neptune
A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition.

7. Moon (or Satellite) An object that orbits a planet
The terms moon and satellite are often used interchangeably, but artificial objects (spacecraft) are usually called satellites and not moons
The terms moon and satellite are often used interchangeably, but artificial objects (spacecraft) are usually called satellites and not moons…
Ganymede (orbits Jupiter)

8. Asteroid Relatively small and rocky object that orbits a star
(1) Note the non-spherical shape; small objects are often non-spherical because their gravity is not strong enough to compress the material into a sphere.
(2) Asteroids are sometimes called minor planets because they orbit much like planets but are smaller than anything we consider to be a true planet.
Also worth pointing out:
(1) Note the non-spherical shape; small objects are often non-spherical because their gravity is not strong enough to compress the material into a sphere.
(2) Asteroids are sometimes called minor planets because they orbit much like planets but are smaller than anything we consider
to be a true planet.

9. Comet A relatively small and icy object that orbits a star
Also worth noting: (1) the basic difference between an asteroid and a comet is composition; (2) comets have tails ONLY when they come close to the Sun, not when they are much farther away.

10. Difference between an asteroid and a comet
the basic difference between an asteroid and a comet is composition;
(2) comets have tails ONLY when they come close to the Sun, not when they are much farther away.

12. Pluto
Also worth noting: (1) the basic difference between an asteroid and a comet is composition; (2) comets have tails ONLY when they come close to the Sun, not when they are much farther away.
A relatively small yellow dog from Disney. “If Pluto is a dog, then what’s Goofy?”
Continuing…

13. Solar (Star) System
A star and all the material that orbits it, including its planets and moons

14. Nebula An interstellar cloud of gas and/or dust
Note: We do not include “nebula” in our list of basic definitions in ch. 1, because it is a less important term at this point in the course. However, you may find yourself talking about nebulae (e.g., Orion Nebula) if you are doing any early-term observing with your students, in which case you may find this slide useful.

15. Galaxy
A great island of stars in space, all held together by gravity and orbiting a common center
Remember that one of the most common student problems is confusion between the terms “solar system” and “galaxy.” You can use these slides of basic definitions to help combat this problem.
M31, the great galaxy
in Andromeda

16. Universe
The sum total of all matter and energy; that is, everything within and between all galaxies

17. How did we come to be?
This slide (Figure 1.2) packs in a lot of basic information. You might go through the frames slowly as follows:
• The universe is expanding, from which we infer a beginning in what we call the Big Bang. Note that, based on the observed rate of expansion, we conclude that the universe is about 14 billion years old. (WMAP results from 2003 were 13.7 ± .2 billion years).
• The expansion continues to this day except where gravity has “won”: stars, galaxies, clusters.
• Galaxies make possible the formation of stars, and recycle material through generations of stars.
• Although the universe began with only the chemical elements H & He, stars have created the elements from which rocky planets are made.
• Life begins from this “star stuff” on at least one particularly friendly planet.

18. The farther away we look in distance,
the further back we look in time.

19. We see the Orion Nebula as it looked 1500 years ago.
Example:
We see the Orion Nebula as it looked 1500 years ago.

20. Question: When will we be able to see what it looks like now?
Example:
This photo shows the Andromeda Galaxy as it looked about 2 1/2 million years ago.
Question: When will we be able to see what it looks like now?
Answer to question: in about 2.5 million years. But point out that for a galaxy, not much will change in that time.
Also worth noting: This photo shows 100,000 years of time, because the galaxy is about 100,000 light-years in diameter. Thus, we see the near side as it was 100,000 years later than the time at which we see the far side.

21. Light-year The distance light can travel in 1 year
About 10 trillion kilometers (6 trillion miles)

22. At great distances, we see objects as they were when the universe was much younger.

23. How far is a light-year?

24. How far is a light-year?
Emphasize that a light-year is a unit of distance NOT a unit of time. Remind students of Common Misconception box in text (p. 6). Equation is optional: it is not given in the book, but should be easy for most students to follow.

25. Why can’t we see a galaxy 15 billion light-years away?
This is an optional question to ask your students, to see if they have grasped the idea of the observable universe.

26. Thought Question Why can’t we see a galaxy 15 billion light-years away
Thought Question Why can’t we see a galaxy 15 billion light-years away? (Assume the universe is 14 billion years old.)
Because looking 15 billion light-years away means looking to a time before the universe existed.
This is an optional question to ask your students to see if they have grasped the idea of the observable universe.

27. Navigating the Universe: Sizes and Scales
“I don’t pretend to understand the Universe. It’s a great deal bigger than I am”
- Thomas Carlyle ( )
Carlyle was a scottish historian

28. 1.2 The Scale of the Universe
Our goals for learning:
How big is Earth compared to our solar system?
How far away are the stars?
How big is the Milky Way Galaxy?
How big is the universe?
How do our lifetimes compare to the age of the universe?

29. Scale models of the Universe
Scale Sun as a grapefruit (1:10,000,000,000)

30. How big is Earth compared to our solar system
How big is Earth compared to our solar system? Let’s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter). How big is Earth on this scale?
an atom
a ball point
a marble
a golf ball
This slide begins our discussion of the scale of the solar system, introducing the 1-to-10 billion scale used in the book. As shown here, a good way to start is to show students the size of the Sun on this scale, then ask them to guess the size of Earth in comparison.
Suggestion: Bring a large grapefruit (or similar size ball) to class to represent the Sun; also have a 1 mm ball bearing to represent Earth for the correct answer to the multiple choice question.

31. Let’s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter). How big is Earth on this scale?
an atom
a ball point
a marble
a golf ball
Here is the answer to the question. Emphasize the incredible difference in size; then ask students to think about how far from the Sun they think Earth would be on this scale…

32. Where are the planets? On this scale, where is the nearest star?
Mercury = grain of sand, 6 meters away (19 feet)
Venus = ball point pen tip, 11 meters (36 feet) away
Earth = tip of ball point pen, 15 meters (49 feet) away
Moon = 4 cm away from Earth
Mars = large grain of sand, 23 meters (75 feet) away
Jupiter = marble, 78 meters (256 feet!)
Pluto (R.I.P.) = head of a pin, 1/3 mile away
15 meters = 49 feet
23 meters = 75 feet
73 meters = 255 feet
On this scale, where is the nearest star?

33. On this scale, the nearest stars would be a triple-star system formed by a cantaloupe, an apple and an orange, located a continent away.
There is essentially nothing in between!!

34. BIG Scale of the Universe kilo- mega- (aka million) NUMBERS
giga- (aka billion)
tera- (aka trillion)
Little
NUMBERS
centi-
milli-

36. Our goals for learning:
1.3 Spaceship Earth
Our goals for learning:
How is Earth moving in our solar system?
How is our solar system moving in the Galaxy?
How do galaxies move within the Universe?
How do these translate to motion in our sky?

37. How is Earth moving in our solar system?
Contrary to our perception, we are not “sitting still.”
We are moving with the Earth in several ways, and at surprisingly fast speeds…
The Earth rotates around its axis once every day.
Our first motion is ROTATION.
Point out that most of us are moving in circles around the axis at speeds far faster than commercial jets travel, which is why jets cannot keep up with the Sun when going opposite Earth’s rotation…

38. Earth orbits the Sun (revolves) once every year:
at an average distance of 1 AU ≈ 150 million km.
with Earth’s axis tilted by 23.5º (pointing to Polaris)
and rotating in the same direction it orbits, counter-clockwise as viewed from above the North Pole.
Our second motion is ORBIT. Point out the surprisingly high speed of over 100,000 km/hr.

39. … And orbits the galaxy every 230 million years.
Our Sun moves randomly relative to the other stars in the local Solar neighborhood…
typical relative speeds of more than 70,000 km/hr
but stars are so far away that we cannot easily notice their motion
… And orbits the galaxy every 230 million years.
Our third and fourth motions are MOTION WITH THE LOCAL SOLAR NEIGHBORHOOD and ROTATION OF THE MILKY WAY GALAXY.

40. More detailed study of the Milky Way’s rotation reveals one of the greatest mysteries in astronomy:
Most of Milky Way’s light comes from disk and bulge …
Although we won’t discuss dark matter until much later in the course, you might wish to mention it now to whet students’ appetites…
…. but most of the mass is in its halo

41. How do galaxies move within the universe?
Galaxies are carried along with the expansion of the Universe. But how did Hubble figure out that the universe is expanding?
Describe the raisin cake analogy, and have students work through the numbers with you to make the table. (E.g., “How far away is Raisin 1 at the beginning of the hour? [1 cm] How far is it at the end of the hour? [3 cm] So how far would you have seen it move during the hour? [2 cm] So how fast is it moving away from you? [2 cm/hr]”

42. Hubble discovered that:
All galaxies outside our Local Group are moving away from us.
The more distant the galaxy, the faster it is racing away.
Conclusion: We live in an expanding universe.
We will revisit this topic again at the end of the class.
Now relate the raisin cake analogy to the real universe…

43. Are we ever sitting still?
Earth rotates on axis: > 1,000 km/hr
Earth orbits Sun: > 100,000 km/hr
Solar system moves among stars: ~ 70,000 km/hr
Milky Way rotates: ~ 800,000 km/hr
Milky Way moves
in Local Group
This slide summarizes our motion with spaceship Earth…
Universe
expands

44. How has the study of astronomy affected human history?
The Copernican revolution showed that Earth was not the center of the universe (Chapter 3).
Study of planetary motion led to Newton’s laws of motion and gravity (Chapter 4).
Newton’s laws laid the foundation of the industrial revolution.
Modern discoveries are continuing to expand our “cosmic perspective.”

45. For next class meeting, read:
Chapter 2
Homework:
Register for MasteringAstronomy (see course website for instructions)
complete Introduction Assignments by Wednesday
If I don’t screw up, you can get a copy of each lecture
slides by 9PM the previous day from the course website 45 45